What temps are the rest water at towards end of lights on time? The more I have to adjust ph in the 5gal, the more unstable it gets over days if you have to really fix a swing. Make sure it's cool, and I'd probably do a full water swap to be sure with fresh nuted water. Since your ph has been rising, let it mix and stablize on the lower side so your daily addbacks will naturally drift the ph back down by volume vs having to add ph down. If you are doing round buckets and the plants get thirsty, you can get black 7 gallon buckets that are just a little deeper with the same top. That extra 2 gallons of water in there really helps stabilize things.
What nutes are you using? Some certainly make ph swing more as do certain addins.